This invention relates to a process for thermally stabilizing steelmaking slag such that it can be used in applications requiring dimensional stability, e.g. as aggregate in road construction and cementitious applications.
Major steelmaking processes such as the basic oxygen furnace operation and the electric arc furnace operation, produce large quantities of slag. A large proportion of this slag is treated as a waste material and there is a great need to be able to adapt this waste material to useful purposes.
In steelmaking, the slag is normally air cooled, crushed and processed to recover the contained metallics. Some of the slag is then recycled to the blast furnace while a significant proportion is used in road construction due to its very high stability and skid and wear resistance. In recent years, however, use of slag in road construction has been quite severely restricted in many regions because of an undesirable expansion of the slag aggregate leading to a rapid deterioration of the roads. The volume expansion of the slag is attributed to the short and long term hydration of contained calcium and magnesium oxides. Because of this problem, a significant proportion of the slag that is now produced is being stockpiled while attempts are being made to resolve the problem and reinstate slag as a viable road construction material or to find other high volume applications for this material.
Systems for treating blast furnace slag have been described in the past and, for instance, Passow, U.S. Pat. No. 747,919 describes a process in which water-granulated blast furnace slag was moistened and then heated to about 1,200.degree. C. The slag was preferably treated with carbon dioxide while being heated so as to produce a highly cementitious material.
In Dresler, U.S. Pat. No. 903,062, a process for producing material for manufacturing bricks is described. In this case, water granulated slag was mixed with ground slag that had been solidified in the open air and this mixture was molded. The molded product was then subjected to the action of carbonic acid under pressure for the purpose of acting on any free lime that was present.
It is the object of the present invention to provide an improved process for the treatment of particles of steelmaking slag such that the particles become dimensionally stable on hydration.